1. Field of the Invention
This invention relates to a pattern recognition apparatus and to a pattern display apparatus each using an optical correlator.
2. Description of the Prior Art
Conventionally, optical pattern recognition has been carried out by the use of a Vander Lugt type optical correlator such as shown in FIG. 1 of the accompanying drawings. This method uses an apparatus in which a correlation filter C is equipped with reference patterns each exhibiting a correlation peak to an input of a specific pattern and in which an input pattern A, a first lens B, the correlation filter C, a second lens D, and an output plane E are arranged in this order, on the focal planes of the lenses. The apparatus judges whether or not the input pattern A is an intended pattern by judging whether the correlation peak value on the output plane is greater or smaller than a predetermined value when the input pattern A is inputted. Furthermore, by the apparatus pattern recognition can be made by finding out the greatest correlation peak value amount the correlation peak values corresponding to the input pattern by the use of a correlation filter having a plurality of reference patterns prepared by multiplex recording and then recording the pattern corresponding to the greatest correlation peak value.
In accordance with the method described above, however, the correlation peaks cannot always be normalized for some input patterns. Therefore, the greatest peak value must be found by a computer or the like in order to make pattern recognition, and the real time operation is difficult.
The same problem occurs in the case of display of a recognized pattern in accordance with this method because the display is based on the prerequisite that the greatest peak value described above is to be found out.
For example, in "OPTICAL ENGINEERING", vol. 26, No. 5 (May 1987), pages 428-433, Eung Gi Paek & Demetri Psaltis, "Optical associative memory using Fourier transform holograms", a method is proposed which improves detection accuracy by recognizing an input pattern optically with an optical correlator, displaying the recognized pattern optically in the form of a reference pattern, and by feeding back this recognition signal to the optical correlator.
However, the method of this prior art described in the above quoted reference involves the problem in that, for example, pattern recognition with sufficiently high detection accuracy cannot be made for input patterns having low degree of correlationship.